Earlier in 2024, Nintendo introduced a new system to its Switch Online 'Missions and Rewards' which requires users to play a retro game before they can purchase icons.
We've seen it with games like Super Mario World and The Legend of Zelda: A Link to the Past and the same "play and redeem" offer is now live for Super Mario Bros.: The Lost Levels. As you can see below, you can currently unlock all sorts of classic icons tied to this particular entry. These icons will be available until 5th August 2024.
"Play this game while the event is active to be able to redeem points for icon elements related to this game...."
Super Mario Bros. The Lost Levels was added to Nintendo's Switch Online NES library back in 2019. Here's a little about this game, and you can see it in action at the top of this page.
Super Mario Bros.: The Lost Levels – Originally released in Japan as Super Mario Bros.® 2, this game has previously made only brief cameo appearances in the Western Hemisphere. Mario fans will appreciate the familiar look and feel of the game, while finding that its updated gameplay creates an entirely new challenge. In addition to the classic enemies already known to fans worldwide, there are also Poison Mushrooms, backward Warp Zones and the occasional wind gust (which can help or hinder your progress).